Gloss-enhancing coating for ink-jet media

ABSTRACT

The present invention is drawn to a composition for cast-coating on ink-jet media. The composition includes a liquid vehicle, silica particulates, and an internal release agent. The composition is substantially free of polymeric binder and can improve the glossiness of a porous particulate-coated ink-receiving media by at least 2 gloss units at 20 degrees. The silica particulates can be suspended in the liquid vehicle at about 1-35 wt %, and can have a particle size of less than about 150 nm. The internal release agent can be present at about 0.5-10 wt %.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/796,639, filed Apr. 27, 2007 now U.S. Pat. No. 8,048,497, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Papers used for ink-jet printing often come in a variety of types ofsurface finishes. Typically, these surface finishes are categorizedaccording to the level of glossiness, such as gloss, semi-gloss, andmatte. In many applications, gloss, even if in a small amount, can bedesirable, such as with photo paper. In such cases, it can be verycostly to formulate coatings that provide an adequate amount of glosswithout losing other desirable qualities of the media such as waterfastness, bleed control, etc. Often times, this requires the use of agreater quantity of materials and/or use of higher-quality or moreexpensive materials. Both can greatly increase the manufacturing costs.Additionally, the use of some materials in coatings prohibits their usewith particular manufacturing methods, such as cast-coating.

It is desirable, therefore, to create an ink-jet media that providesglossiness without adversely affecting desirable properties of themedia. It is also desirable to provide the media in a manner that can beeasily manufactured and does not drastically increase the cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particular processsteps and materials disclosed herein because such process steps andmaterials may vary somewhat. It is also to be understood that theterminology used herein is used for the purpose of describing particularembodiments only. The terms are not intended to be limiting because thescope of the present invention is intended to be limited only by theappended claims and equivalents thereof.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise.

As used herein, “liquid vehicle” refers to the fluid in which silica canbe dispersed to form a composition in accordance with embodiments of thepresent invention. Many liquid vehicles and vehicle components are knownin the art. Typical liquid vehicles can include a single substance or amixture of a variety of different agents, such as co-solvents, buffers,and viscosity modifiers. In one embodiment, the liquid vehicle cancomprise or consist essentially of water.

“Base paper” includes any unextruded or uncoated paper that can includefibers, fillers, and/or additives, etc. Examples of fillers andadditives include wood, clay, kaolin, calcium carbonate, gypsum,titanium oxide, talc, alumina trihydrate, magnesium oxide, minerals,synthetic fillers, natural fillers, and combinations thereof.

“Substrate” includes any base material that can be coated in accordancewith an embodiment of the present invention, such as base paper or otherpaper substrates, film base substrates, polymeric substrates, and thelike. Further, pre-coated substrates, such as substrates coated with aporous-particulate ink-receiving layer, can also be used in embodimentsof the present invention as well.

As used herein, the term “gloss” refers generally to the amount of lightreflected by an object's surface, such as an ink-jet media surface.Gloss can be quantified, as is common in the art, and is measuredrelative to specific specular angles from an object surface. Thespecular angle is the angle equal to but opposite the angle ofincidence. This specular light is responsible for the highlights visibleon shiny materials. When quantifying gloss, it can be measured at anglesof 20 degrees, 60 degrees, and 85 degrees off of the normal.Additionally, another angle of measurement, known as TAPPI Gloss, ismeasured at 75 degrees off the normal. ASTM Designation D523 specifiesthat a 60 degree measurement angle may be used for most materials. Thetest method recommends the use of a 20 degree measurement angle when the60 degree gloss value is greater than 70, which indicates ahighly-reflective material. The use of an 85 degree measurement angle isrecommended when the 60 degree gloss value is less than 10, whichindicates a less-reflective material. Gloss measurements are indicatedby gloss units in relation to the angle used for measurement.

As used herein, “wetting agent” refers to a type of surface activeagent. Such agents are typically amphipathic molecules consisting of anonpolar hydrophobic portion, which is attached to a hydrophilic polaror ionic portion. Wetting agents can be used in the present invention todisperse components of the composition, such as the internal releaseagent and/or silica particulates.

“Internal release agent” refers to substances that are added into aliquid coating and which migrate to an interface to control or eliminateadhesion between two surfaces. Internal release agents act by lesseningintermolecular interactions between two surfaces in contact, e.g. coatedpaper and coating drum, or by preventing such close contact between twosurfaces. Internal release agents can be materials based on aliphatichydrocarbon or fluorocarbon groups, and/or they can be particulatesolids. Non-limiting examples of internal release agents can includecertain types of waxes, fatty acid metal soaps, long-chain alkylderivatives, polymers, and fluorinated compounds. Internal releaseagents will also tend to phase separate from the liquid.

As used herein, “gsm” represents grams per square-meter.

As used herein, a plurality of components may be presented in a commonlist for convenience. However, these lists should be construed as thougheach member of the list is individually identified as a separate andunique member. Thus, no individual member of such list should beconstrued as a de facto equivalent of any other member of the same listsolely based on their presentation in a common group without indicationsto the contrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 0.01 to 2.0” should beinterpreted to include not only the explicitly recited values of about0.01 to about 2.0, but also include individual values and sub-rangeswithin the indicated range. Thus, included in this numerical range areindividual values such as 0.5, 0.7, and 1.5, and sub-ranges such as from0.5 to 1.7, 0.7 to 1.5, and from 1.0 to 1.5, etc. This same principleapplies to ranges reciting only one numerical value. Furthermore, suchan interpretation should apply regardless of the breadth of the range orthe characteristics being described.

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particular processsteps and materials disclosed herein because such process steps andmaterials may vary somewhat. It is also to be understood that theterminology used herein is used for the purpose of describing particularembodiments only. The terms are not intended to be limiting because thescope of the present invention is intended to be limited only by theappended claims and equivalents thereof.

With this in mind, it has been recognized that it would be advantageousto provide a composition for coating a substrate that can improve glosswithout adversely affecting the print quality of the substrate. Further,the composition can be formulated for use with cast-coating, that willallow for a media with a fine gloss finish to be removable from acast-coating drum. In one embodiment, a composition for cast-coating onink-jet media can include a liquid vehicle, a plurality of silicaparticulates suspended in the liquid vehicle, and an internal releaseagent. The silica particulates can be present in an amount from about 1wt % to about 35 wt %. Silica particulates of the present invention canbe of a size less than about 150 nm. The internal release agent can bepresent in an amount from 0.5 wt % to 10 wt %. The coating can besubstantially free of any polymeric binder. When cast-coated over aporous particulate-coated ink-receiving media to a coat weight of lessthan 2 gsm, the coating can produce an increase in the gloss of themedia of at least 2 gloss units at 20 degrees. Further, the coating canbe formulated so as to have a surface energy greater than the surfaceenergy of a cast-coating drum used to apply the composition.

In one aspect, the composition can further include a wetting agentdispersed in the liquid vehicle. Such wetting agent can be utilized toassist the coating to properly wet the paper. Where the coat weight isgenerally low, the wetting agent can be used to more evenly spread thecomponents of the composition onto the media. Therefore, the wettingagent can assist in wetting the media. In other words, the wetting agentcan help the coating to spread on the media by altering the surfaceenergy of the liquid.

The wetting agent can also serve to keep the internal release agent inthe composition. Many commercially-available internal release agents aresold in water-based emulsions that include wetting agents. The wettingagents can be particularly useful with primarily-hydrophobic internalrelease agents such as, for example, calcium stearate. Wetting agentscan essentially stick to the surface of the hydrophobic internal releaseagent and keep them suspended in the liquid vehicle. Wetting agents canalso improve compositions by stabilizing the compositions generally,e.g. effectively improving the suspension of substantially allparticulate components. Therefore, the addition of wetting agents to thecomposition can prevent the components from aggregating and/or floatingto the top or sinking to the bottom of the composition.

As described, the composition includes an internal release agent. Suchinternal release agent can consist of or comprise a single internalrelease agent, or a plurality of internal release agents. The primaryrole of the internal release agent is to migrate to the interfacebetween the coating and the casting drum in order to modify the surfaceenergy of the interface so as to allow for proper release from thecasting drum. Such modification of the interface allows for a smoothprocessing run of direct cast-coating the composition onto a mediasubstrate. Adding an internal release agent will typically reduce thewettability of the coating on the cast-coating drum. The internalrelease agent can reduce the wettability of the coating by making thespreading coefficient of the coating on the cast-coating drum negative.However, there is a point when the liquid interface is highly crowdedand does not allow for room for additional internal release agent tohave an impact on the surface tension. Such state is known as thecritical micelle concentration. The critical micelle concentration ofmany coated gloss compositions in accordance with embodiments of thepresent invention can be from about 30 dynes/cm to about 35 dynes/cm.

The amount of internal release agent used is dependent on a variety offactors. Enough internal release agent should be used so as to cause thecoated media substrate surface energy (including the uppermostgloss-improving coat) to have a surface energy greater than the surfaceenergy of the cast coating drum. This difference in the surface energyensures proper release of the coated media substrate from thecast-coating drum. Thus, the coating can be effectively used in acast-coating process. The surface energy of the gloss-improvingcomposition can, therefore, vary at least according to the casting drum.Casting drums can be composed of a variety of materials, typicallymetals and alloys. Casting drums may also include a coating, such as anoxide layer, which can alter the surface energy of the casting drum.

In accordance with embodiments of the present invention, variousinternal release agents can be used in the gloss-improving compositions.Internal release agents can be organic or inorganic. Non-limitingexamples of internal release agents include metal stearates,polyethylene emulsions, beef tallow, waxes, ketene dimmer, fatty acidmetal soaps, and sulfonated oil surfactants. In one embodiment, theinternal release agent can be a wax, such as a petroleum, vegetable,animal, and/or synthetic wax. Non-limiting examples of metal stearatesinclude calcium stearate and magnesium stearate. In a specificembodiment, the internal release agent can comprise or consistessentially of calcium stearate. The internal release agent can includea single internal release agent or a plurality of internal releaseagents.

The silica used in the gloss-improving composition can be a variety offorms. Preferably, the silica is of a particle size of less than about150 nm. Such measurement is based on dynamic light scattering, andindicates the average particle size. In one embodiment, the silica cancomprise or consist essentially of colloidal silica. In anotherembodiment, the silica can comprise or consist essentially of fumedsilica. In still another embodiment, the silica can comprise or consistessentially of precipitated grades of silica. In yet another embodiment,the silica can comprise or consist essentially of gelled grades ofsilica. The silica can be treated or processed prior to use. In oneaspect, the silica can be nanomilled to the preferred size. Such millingis often particularly useful with gelled and precipitated forms ofsilica.

In one embodiment, the silica can be cationic. The silica can be treatedby any of the techniques known in the art to produce a cationic silica,including but not limited to treatment by aluminum chlorohydrate orvarious aminosilane compounds. By including cationic silica in thegloss-improving composition, the resulting coating will show an improveddye adhesion, thus improving overall print performance. Improved dyeadhesion can improve many coating properties; more specifically, it candecrease bleed and generally improve color performance.

In accordance with these embodiments, various details are providedherein which are applicable to each of the coating composition, printingmedia, and associated methods. As such, general discussion of any one ofthese embodiments is relevant to the other embodiments.

A method for improving gloss on ink-jet media can include applyingcertain coatings to a substrate. The substrate can include a porousparticulate-coated ink-receiving layer coated thereon. If not, then suchcoating can be applied on a substrate. Onto the ink-receiving layer, agloss-improving composition as discussed herein, including a liquidvehicle, silica particulates, and internal release agent, can becast-coated thereon. The gloss-improving composition can be applied to acoat weight of less than about 2 gsm. In one embodiment, the compositioncan be applied to a coat weight of less than about 1 gsm. In anotherembodiment, the gloss-improving composition can be applied to a coatweight of about 0.5 gsm to about 2 gsm.

The substrate can be a variety of materials. Most substrate materialsare known in the art. Non-limiting examples of materials that can beused as substrate include filled- and non-filled raw base paper, whichmay include fibers, fillers, additives, etc. Examples of fillers andadditives include wood, clay, kaolin, calcium carbonate, gypsum,titanium oxide, talc, alumina trihydrate, magnesium oxide, minerals,synthetic fillers, natural fillers, and combinations thereof. Inaddition to the ink-receiving layer, the substrate can includeadditional coatings, such as a curl control layer. In one embodiment,the coated substrate can be ink-jet ink printing media. In anotherembodiment, the ink-jet printing media can be photo paper.

As the function of the gloss-improving composition is to improve gloss,it is preferable, although not required, that the ink-receiving layerthat is overcoated with the gloss-improving composition should have somegloss itself. In one aspect, the gloss-improving composition can improvegloss by at least 2 gloss units at 20 degrees. In other embodiments, thegloss-improving composition can produce a gloss increase of at least 5gloss units at 20 degrees. In still other embodiments, thegloss-improving composition can produce a gloss increase of at least 10,or at least 15, or at least 20 gloss units, all measured at 20 degrees.

In one aspect, the substrate with the porous particulate-coatedink-receiving layer can be calendared prior to cast-coating thegloss-improving composition thereon. Such calendaring, in many cases,can increase the level of improvement in gloss seen when thegloss-improving composition is applied. In one embodiment, the gloss ofan uncalendared ink-receiving layer can be increased by about 2 to about10 gloss units at 20 degrees when the gloss-improving composition isapplied. In another embodiment, the gloss of a calendared ink-receivinglayer can be increased by about 15 to about 30 gloss units at 20 degreeswhen the gloss-improving composition is applied.

In accordance with additional embodiments of the present invention, anink-jet media can include a substrate, porous particulate-coatedink-receiving layer coated on the surface of the substrate, and agloss-enhancing composition coated onto the ink-receiving layer. Thegloss-enhancing composition can increase the gloss by at least 2 glossunits at 20 degrees over the gloss of the porous particulate-coatedink-receiving media.

By coating an ink-receiving layer with the gloss-enhancing compositiontaught above and herein, the glossiness of the media can be improved.Such improvement can occur regardless of many of the features of theink-receiving layer. As such, the gloss-enhancing composition can beused as an effective tool to improve the quality of many ink-jet mediasubstrates, including those of lower-quality. The gloss-improvingcomposition can be used in small amounts (e.g. coat weight less thanabout 2 gsm), and therefore does not require great expenditure for thegloss improvement. Furthermore, the relatively thin layer of thecomposition effectively maintains the image quality of the ink-receivinglayer on the media. Additionally, the composition can be used in directcast-coating, as it can be formulated so as to properly release from acasting drum.

EXAMPLES

The following examples illustrate embodiments of the invention that arepresently known. Thus, these examples should not be considered aslimitations of the present invention, but are merely in place to teachhow to make the best-known compositions of the present invention basedupon current experimental data. As such, a representative number ofcompositions and their method of manufacture are disclosed herein.Unless specific cast coating equipment is noted, the examples werecoated using a simulated cast-coating method, wherein a thin layer ofcomposition is coated on the media and pressed against a mirror-polishedand heated chrome plate. The coated media is held in contact with theheated plate. In plant-scale cast coating operations, a composition isapplied to a media and the media is then stretched over a heatedmirror-polished chrome drum to cast the coat.

Example 1 Preparation of Gloss-Improving Composition

A composition was prepared by mixing 1000 g of cationic colloidal silicahaving a mean particle diameter of 100 nm, 0.02 g ofnonylphenoxypolyglycidol, and 15 g of calcium stearate emulsion. Thecomponents were mixed in a beaker and stirred using an overhead mixerfor approximately 20 minutes to ensure full incorporation of thematerials.

Example 2 Coating Composition onto Media

The composition of Example 1 was coated using a Meyer Rod drawdown ontotwo different types of ink-jet paper—one type calendared and the othertype uncalendared. Both papers include a porous-type ink-receiving layerincluding silica, binder and surfactant. The coating of eachgloss-improving composition was to a coat weight of 0.5 gsm.

Example 3 Gloss Measurements

The ink-jet papers used in Example 2 were measured for gloss at 20degrees before and after the application of the gloss-improvingcomposition. The results are in Table 1.

TABLE 1 Gloss before Gloss after gloss-improving gloss-improving Medialayer* layer* Uncalendared 1 1.8 3.7 Uncalendared 2 1.8 11.2 Calendared1 4.2 23.3 Calendared 2 4.2 31.4 *Gloss measurements at 20 degrees andreported in gloss units.

Example 4 Preparation of Gloss-Improving Composition

A larger batch of gloss-improving composition was made according to theprocedure of Example 1. However, in this case, the mixture used 234 kgof cationic colloidal silica having a mean particle diameter of 558 nm,4.7 g of nonylphenoxypolyglycidol and internal release agent.

Example 5 Coating Composition onto Media

The formulation of Example 4 was cast-coated onto three base papers(labeled A, B, and C) which were pre-coated with a porous inkjet coatingcomprising silica, binder and surfactants. The coating of eachgloss-improving composition was to a coat weight of less than 1.5 gsm.

The coating was done using a plant-scale chrome coating roll running ata webspeed of 35 feet per minute, drum temperature of 160° F. and nippressure of approximately 300 psi.

Example 6 Gloss Measurements

The ink-jet papers coated in Example 5 were measured for gloss at 20degrees before and after the application of the gloss-improvingcomposition. The results are in Table 2.

TABLE 2 Gloss before Gloss after Coat Weight gloss-improvinggloss-improving Media (gsm) layer* layer* Base A 1.17 4.1 32.0 Base C0.67 4.0 33.0 Base D 0.33 9.5 38.9 *Gloss measurements at 20 degrees andreported in gloss units

Example 7 Preparation of Gloss-Improving Composition

A composition was prepared by mixing 100 g of cationic colloidal silica(32 wt % solids dispersion), with a mean particle diameter of 50 nm,0.02 g of nonylphenoxypolyglycidol surfactant, and 1.5 g of calciumstearate emulsion (53 wt % solids) and sufficient water to bring thetotal solids of the coating composition to 14%. The components weremixed in a beaker and stirred to ensure full incorporation of thematerials.

Example 8 Coating Composition onto Media

The composition of Example 7 was coated using a #2.5 Meyer Rod drawdownonto a pre-coated porous ink-jet paper. This base paper precoatedcomprised silica, binder and surfactants. The coating of thegloss-improving composition was to a coat weight of 1 gsm. Afterapplication using the meyer rod, the sheet was cast against a heated(60° C.) mirror-finish chrome plate using a roller to simulate aplant-scale cast-coating system.

Example 9 Gloss Measurements

The ink-jet paper prepared in Example 8 was measured for gloss at 20 and60 degrees before and after the application of the gloss-improvingcomposition. The results are in Table 2. The results are averages of 3measurements each and represent a statistically significant difference(p=0.02)

20° Gloss 60° Gloss 20° Gloss 60° Gloss before gloss- before gloss-before gloss- before gloss- improving improving improving improvingMedia layer* layer* layer* layer* Ex 7 4 21 5 30 *Gloss measurements at20 degrees and reported in gloss units.

While the invention has been described with reference to certainpreferred embodiments, those skilled in the art will appreciate thatvarious modifications, changes, omissions, and substitutions can be madewithout departing from the spirit of the invention. It is intended,therefore, that the invention be limited only by the scope of thefollowing claims.

What is claimed is:
 1. A composition for cast-coating on ink-jet mediausing a cast-coating drum, comprising: a liquid vehicle; a plurality ofsilica particulates suspended in the liquid vehicle in an amount ofabout 1 wt % to about 35 wt %, said silica particulates having aparticle size less than about 150 nm; and from 0.5 wt % to 10 wt % ofinternal release agent, wherein the composition is substantially free ofa polymeric binder, and wherein the composition, when cast-coated on aporous particulate-coated ink-receiving media to a coat weight of lessthan 2 gsm, produces a gloss increase of at least 2 gloss units at 20degrees over the gloss of the porous particulate-coated ink-receivingmedia, and wherein the composition has a surface energy greater than thesurface energy of the cast-coating drum.
 2. A composition as in claim 1,further comprising a wetting agent dispersed in the liquid vehicle.
 3. Acomposition as in claim 1, wherein internal release agent is selectedfrom the group consisting of metal stearates, polyethylene emulsions,beef tallow, waxes, ketene dimmer, fatty acid metal soaps, andsulfonated oil surfactants.
 4. A composition as in claim 1, wherein theinternal release agent includes calcium stearate.
 5. A composition as inclaim 1, wherein the liquid vehicle includes water.
 6. A composition asin claim 1, wherein the silica includes cationic silica.
 7. Acomposition as in claim 1, wherein the silica includes colloidal silica.8. A composition as in claim 1, wherein the silica includes fumedsilica.
 9. A composition as in claim 1, wherein the silica includesnanomilled precipitated or gelled silica.
 10. A composition as in claim1, wherein the internal release agent includes more than one internalrelease agent.